1. Field of the Invention
The present invention pertains to the transducing (e.g., recording and reproduction) of information on/from magnetic tape, and particular to a structure of a scanner (e.g., drum or rotor) for a helical scan tape drive.
2. Related Art and other Considerations
In magnetic recording on tape using a magnetic tape drive, relative motion between a scanner [typically a drum or rotor with both one or more write element(s) and one or more read element(s)] and the tape causes a plurality of tracks of information to be transduced with respect to the tape. The magnetic tape is typically housed in a cartridge which is loaded into the tape drive. The tape extends between a cartridge supply reel and a cartridge take-up reel. The tape drive typically has a supply reel motor for rotating the cartridge supply reel and a take-up reel motor for rotating the cartridge take-up reel.
After the cartridge is loaded into the tape drive, the tape is extracted by mechanisms in the drive so that a segment of the tape is pulled from the cartridge and into a tape path that travels proximate the scanner. The extraction mechanisms take the form of tape guides which are mounted on trolleys. During the extraction operation, trolley motors move the trolleys along a predefined trolley path, so that the tape guides which surmount the trolleys displace the tape into the tape path as the trolleys travel along the trolley path. When the trolleys reach the full extent of travel along the trolley path, the tape is proximate the scanner. Thereafter the tape can be transported past the scanner, e.g., by activation of a capstan and/or the supply reel and take-up reel motors, depending upon the particular type of transport mechanisms employed.
In a helical scan arrangement, as the magnetic tape is transported the magnetic tape is at least partially wrapped around the rotating scanner so that heads (both write heads and read heads) positioned on the scanner are contiguous to the scanner as the scanner is rotated. One or more write heads on the scanner physically record data on the tape in a series of discrete tracks of stripes oriented at an angle with respect to the direction of tape travel. As the tape is transported past the scanner, information can be transduced to or from the tape by the tape drive in recording and reading operations, respectively. The data is formatted, prior to recording on the tape, to provide sufficient referencing information to enable later recovery during readout by one or more read heads. Examples of helical scan tape drives are shown, inter alia, in the following U.S. patents (all of which are incorporated herein by reference): U.S. Pat. No. 4,835,628 to Hinz et al.; U.S. Pat. No. 4,843,495 to Georgis et al.; U.S. Pat. No. 5,065,261 to Hughes et al.; U.S. Pat. No. 5,068,757 to Hughes et al.; U.S. Pat. No. 5,142,422 to Zook et al.; and U.S. Pat. No. 5,602,694 to Miles et al. (which discloses a capstanless helical scan tape drive).
Virtually all multi-headed (i.e., more than 4 magnetic write and/or read heads) helical scanners have the write and read heads themselves xe2x80x9cgroupedxe2x80x9d in logical and often xe2x80x9csymmetricxe2x80x9d ways. This helps to minimize the number of support structures required. FIG. 1 shows an example of a D-2 Video helical scanner configuration with a total of four write heads in two pairs mounted 180 apart and a total of four read heads in two pairs also mounted 180 apart and shifted 90 from the write heads. Each pair of write heads is mounted on a fixed support structure, and each pair of read heads is mounted on an independently moveable actuator.
It has also been found that at high track density it is beneficial to cluster all the write heads of a helical scanner into one single localized group so that the subtle dynamic effects from mechanical part tolerances, assembly tolerance, bearing tolerances/imperfections, etc. affect all write heads (and their written tracks) quasi-equally (see, for example, Section 6, FIG. 12 of xe2x80x9cA High Density Recording Technology for Digital VCRsxe2x80x9d, Consumer Electronics, Vol. 36, No. 3, August 1990). In a similar vein, a particular helical scanner configuration is shown in FIG. 2 shows a scanner configuration in which all of the write heads are clustered into a single localized group and all of the read heads are clustered into a single localized group. In the FIG. 2 configuration, the clustering of all of the write heads into a single localized group has the effect of minimizing the number of support structures is minimized, and all of the written tracks are affected quasi-equally by the subtle dynamic effects. Moreover, the FIG. 2 configuration""s clustering of all of the read heads into a single localized group reduces the number of support structures (i.e., actuators) to only one.
However, mounting all of the read heads onto a single actuator reduces the amount of allowable actuator positioning error that can be tolerated while still keeping all four read heads simultaneously within the boundaries of the written tracks that they are reading.
What is needed therefore, and an object of the present invention, is a scanner (e.g., drum or rotor) having a configuration having of heads which, for a given track density, allows greater allowable actuator positioning errors and/or a larger head positioning error tolerances.
A scanner for use in a helical scan magnetic transducing apparatus has a periphery upon which plural read tranducing elements and plural write transducing elements are mounted non-symmetrically. The plural write transducing elements are physically situated on the periphery of the scanner in M number of local groups, wherein the plural read transducing elements are physically situated on the periphery of the scanner in N number of local moveable groups, and wherein M less than N. Each of the moveable groups has a separate actuator for adjusting position of the group. Various configurations of scanners with differing M and N parameters are disclosed and within the ambit of the invention.